The present invention relates to a surveying device. In particular, the invention relates to a surveying device with a tracking function and also relates to an automatic tracking method by using the surveying device.
In the past, a surveying device with a tracking function has been known, which can measure a distance, a horizontal angle and a vertical angle. Such type of surveying device is so designed that an object reflector (target) such as a corner cube is collimated through a collimating telescope provided on the surveying device, a tracking light is projected from the collimating telescope, and a reflection light from the target is received and detected. When the target moves, a deviation between a detecting position of the reflection light from the target and a center of collimation is identified, and the collimating direction is adjusted based on the deviation, and the target is automatically tracked.
Normally, in this type of surveying device with the tracking function, no operator is assigned on the surveying device side. The target is supported by a surveying operator, or the target is mounted on a construction machine such as a bulldozer. Corresponding to the progress of the surveying operation, the target is moved, and the surveying device tracks the moving target.
However, in case the moving speed of the target exceeds the following speed of the surveying device and the target may be deviated from visual field of the collimating telescope, or in case a reflection light from a reflecting object such as window glass may enter the surveying device, or in case targets pass each other and reflection lights from two or more targets may enter the surveying device, or in case an object such as an automobile may pass in front of the target and may intercept the reflection light, the survey device may miss the target or may erroneously recognize the target and may not be able to track the target, and automatic tracking may be interrupted.
This is because the collimating telescope generally in use has a field angle (angle of visual field) as small as about 1° and a detection range to detect the reflection for automatic tracking is small.
When tracking operation is interrupted, the surveying device starts an operation to search the target. In the searching operation, the collimating telescope is rotated within a predetermined range in vertical direction and in left-to-right direction for scanning while projecting a tracking light, and the target is detected.
The field angle (angle of visual field) of the collimating telescope is as small as about 1°. In order to re-detect the target, it is necessary to have finer pitch of scanning and to increase the number of scanning operations. Therefore, when the tracking operation is interrupted, relatively long time is required until the target can be detected again and the tracking can be started. Further, in the working conditions where the interruption of an optical path caused by an obstacle may occur frequently, a problem may arise that a working efficiency of the measurement is extremely decreased.
Also, in case the target is extensively deviated from the visual field of the telescope, the target may not be detected again, and the surveying operation itself may be stopped.
The surveying device with the tracking function is disclosed in each of JP-A-7-198383, JP-A-2000-346645, and JP-A-2004-170354.